Yep, just set 'Daytime' and 'At night" to the same color temperature. You will not be able to use anything warmer than 2700K though unless you are constantly changing your Location in order to continually fool f.lux into thinking that you live where the sunset has occurred already.

It might be better though to just lower your monitor's brightness using its onboard controls so that you can preserve color accuracy while also reducing eyestrain. Also, make sure your indoor lighting (in the computer room) isn't too dark. It's best to have your indoor lights be bright enough so that it forms a nice balance with the brightness of your monitor. If your monitor is the brightest thing in your field of vision, then your risk of eyestrain dramatically increases. It increases even more if you're using the computer in total darkness.